docs(6209): twelve more test files say which behaviour they pin

shape ledger, MCP projects/search/rulebooks tools, backup, chunking,
plugin context, derived mirror, rule band, shape form gate, plugin
version mint and note usage tests drop issue, milestone and rule numbers,
dates and one-install figures from docstrings, comments and messages.
Three shape-form-gate test names that told the discovery story now name
the property: a registry module's helpers are not service functions, the
divergence gate silences only a family contradiction, and callable helpers
beside a callable canon still prompt. The rulebook tool-count comment that
logged each milestone's additions is replaced by the reason it is a count.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_chunking.py

@@ -1,9 +1,9 @@
-"""chunk_document — the document shape a record is embedded as (#280).
+"""chunk_document — the document shape a record is embedded as.
 
-The model window is 512 tokens and fastembed truncates silently, so before
-chunking, everything past ~400 words of a record was PERMANENTLY invisible to
-semantic search. These tests pin the two halves of the fix's contract: short
-records keep the exact historical shape (the corpus's sharpest vectors are
+The model window is 512 tokens and fastembed truncates silently, so without
+chunking everything past ~400 words of a record would be invisible to
+semantic search. These tests pin the two halves of the contract: short
+records keep the single-document shape (the corpus's sharpest vectors are
 untouched), and long records lose NOTHING — every line of the body lands in
 some chunk, each chunk inside the window budget, each carrying the title as
 its topical anchor.
@@ -29,7 +29,7 @@ def _long_section(tag: str, paragraphs: int = 6, sentence: str = None) -> str:
 
 def test_a_short_record_yields_exactly_the_historical_shape():
     """Snippets and reference notes are the sharpest records in the corpus
-    (#2485) precisely because of this shape — chunking must not touch them."""
+    precisely because of this shape — chunking must not touch them."""
     assert chunk_document("A title", "A short body") == [
         embedding_text("A title", "A short body")
     ]
@@ -54,8 +54,8 @@ def test_a_record_exactly_at_budget_stays_whole():
 
 
 def test_every_line_of_a_long_body_lands_in_some_chunk():
-    """The point of #280. Before chunking, a 2,000-word dev-log's last three
-    quarters could not influence retrieval at all. Nothing may be dropped."""
+    """The point of chunking: every part of a 2,000-word dev-log can
+    influence retrieval. Nothing may be dropped."""
     sections = [
         f"## Topic {i}\n\n{_long_section(f'topic-{i}')}" for i in range(8)
     ]
@@ -139,12 +139,11 @@ def test_a_monster_single_paragraph_is_hard_split_not_dropped():
     assert total_words == 2000
 
 
-# --- no chunk is a heading alone (#4784) -------------------------------------
+# --- no chunk is a heading alone ---------------------------------------------
 #
-# Found by judging live auto-inject menus: "## Work log — 2026-08-21",
-# "## Findings worth carrying forward" and "Two dev→main PRs this session."
-# were each a whole chunk, and took ranks 1–3 on vague queries — text about
-# nothing embeds close to everything. Each case below is one of those shapes.
+# A heading or a one-line preamble as a whole chunk ranks at the top of vague
+# queries — text about nothing embeds close to everything. Each case below is
+# one of those shapes.
 
 _HEADING = re.compile(r"^#{1,6}\s")
 
@@ -220,7 +219,7 @@ def test_a_continuation_piece_repeats_the_heading_it_sits_under():
         assert "## Child" in chunk
 
 
-# --- the read path: best chunk wins (#280 step 4) ----------------------------
+# --- the read path: best chunk wins ------------------------------------------
 
 
 async def test_search_collapses_chunk_rows_to_best_chunk_per_note():
@@ -233,7 +232,7 @@ async def test_search_collapses_chunk_rows_to_best_chunk_per_note():
 
     note_a, note_b = MagicMock(id=1), MagicMock(id=2)
     # Rows are (Note, distance, chunk_index, chunk_text) — the chunk columns
-    # ride along so the collapse can report WHICH passage won (#4243).
+    # ride along so the collapse can report WHICH passage won.
     rows = [
         (note_a, 0.10, 3, "the passage that actually matched"),
         (note_b, 0.20, 0, "b's best"),
@@ -259,19 +258,19 @@ async def test_search_collapses_chunk_rows_to_best_chunk_per_note():
 
     # And the winning chunk is reported, not merely used for scoring. Without
     # this a caller can only preview the head of the body — a span this query
-    # has already ranked lower than the one that won (#4243).
+    # has already ranked lower than the one that won.
     assert report["best_chunk"][1] == {
         "index": 3, "text": "the passage that actually matched",
     }
     assert report["best_chunk"][2]["index"] == 0
 
 
-# --- the write path: one row per chunk (#280 step 3) -------------------------
+# --- the write path: one row per chunk ---------------------------------------
 
 
 def _session_ctx(log_rows=()):
     """A session stand-in. `log_rows` answers the work-log read a task's
-    document now needs (#4251) — answered explicitly rather than left to
+    document needs — answered explicitly rather than left to
     autovivify, because `list(result.all())` on a bare MagicMock raises and is
     swallowed, which would quietly make every one of these a no-log test."""
     from unittest.mock import AsyncMock, MagicMock
@@ -318,9 +317,9 @@ async def test_upsert_stores_one_versioned_row_per_chunk():
 
 
 async def test_a_tasks_work_logs_reach_the_rows_it_is_stored_as():
-    """The wiring half of #4251: the shaper is pure and tested next door, so
-    what is pinned here is that the WRITER actually asks for the logs and
-    embeds what comes back. A log that is written, readable (#4241) and absent
+    """The wiring half: the shaper is pure and tested next door, so what is
+    pinned here is that the WRITER actually asks for the logs and embeds what
+    comes back. A log that is written, readable and absent
     from the index is the same half-surface one layer down."""
     import datetime
     from unittest.mock import AsyncMock, patch
@@ -380,7 +379,7 @@ async def test_backfill_reembeds_notes_with_a_stale_chunker_version():
     session, ctx = _session_ctx()
     # The opening scan, in order: ids already at the current version, every
     # note id, vectors older than their note, tasks logged since their vectors.
-    # IDS ONLY — the text is re-read per note at embed time (#4262).
+    # IDS ONLY — the text is re-read per note at embed time.
     session.execute = AsyncMock(side_effect=[
         _ids(1),            # note 1 is current
         _ids(1, 2),         # the corpus
@@ -402,7 +401,7 @@ async def test_backfill_reembeds_notes_with_a_stale_chunker_version():
 
 
 def test_a_row_is_current_only_in_the_live_models_space():
-    """#4132: the column is a width, not an identity, so a same-width model
+    """The column is a width, not an identity, so a same-width model
     swap writes a second geometry with no error. The backfill's "current"
     predicate has to name BOTH halves of the stamp, on every embedding table."""
     from scribe.models.embedding import (